Fiber optic hydrophones that respond to acoustic signals have shown increasing promise for the acquisition of data, particularly in seismic exploration and other applications. Known fiber optic hydrophones used such applications are based on altering the optical path length of an optical fiber as a function of the acoustic signal. Systems which employ such hydrophones may also include interferometers which detect changes in optical phase or spectrometers which detect spectral shifts. For example, certain fiber optic interferometric sensors respond to underwater perturbations such as acoustic wave fronts by varying the effective length of the fiber optic filament in response to the perturbation.
In such applications, optical fibers are made sensitive to these acoustic waves. An optical fiber exposed to such phenomena changes the medium through which a light or infrared beam passes that is guided by the fiber. One well known technique to implement this concept involves winding an optical fiber around a compliant mandrel. When subjected to an acoustic signal, the geometry of the mandrel varies in direct response to the acoustic signal, and consequently the optical path length of the optical fiber wound around the mandrel.
While effective in changing the effective optical path length of the optical fiber in response to the phenomenon to be measured, these known structures are not easily incorporated into a seismic cable due to their size and geometry. Other known structures, referred to in the art as "clamshells", were designed specifically with size and geometry in mind, but would be improved if they only had greater sensitivity to the acoustic signal.
Thus, there remains a need for a sensor that is responsive to variations in pressure, in the form of a seismic signal, using variations in the stress on a fiber optic element. Such a sensor should be robust, highly sensitive, and easily manufactured.